Quantum Cascade Lasers (QCLs) are semiconductor devices that, currently, have been observed to emit radiation from ~ 2.6 µm to 250 µm (1 to 100 terahertz range of frequencies). They have established themselves as the laser of choice for spectroscopic gas sensing in the mid-wavelength infrared (3-8 µm) and long-wavelength infrared (8-15 µm) region. In the 4-12 µm wavelength region, the highest performing QCL devices, in terms of wall-plug efficiency and continuous wave operation, are indium phosphide (InP) based. The ultimate goal is to incorporate this InP-based QCL technology to silicon (Si) substrate since most opto-electronics are Si-based. The main building blocks required for practical QCL-on-Si integrated platforms were demonstrated and will be covered in this presentation. The experimental results of a 40-stage indium phosphide based quantum cascade laser grown on a lattice-mismatched germanium-coated silicon substrate with metamorphic buffer (M-buffer) is discussed. The QCL's strain-balanced active region was composed of Al0.78In0.22As/In0.73Ga0.27As and an 8 µm-thick all-InP waveguide. Since the M-buffer was insulating, the wafer was processed into ridge-waveguide chips with lateral current injection scheme. Lasing was observed from 78K up to 170K for QCL-on-Si devices. Also discussed is the first room temperature operation of QCL grown on a lattice-mismatched gallium arsenide (GaAs) substrate with metamorphic buffer (M-buffer). Similar to QCL-on-Si, a lateral injection scheme was utilized since M-buffer was insulating. Lasing was observed from 78K up to 303 K for QCL-on-GaAs. Material characterization of QCL-on-InP, QCL-on-GaAs, and QCL-on-Si using Transverse Electron Microscopy (TEM) will also be covered in this presentation. A very small section, 10 µm x 10 µm, of the QCL active region was used to give an estimate of the defect density for each of the QCL configuration. Lastly, characterization of the material quality of the remaining 6-inch wafer of QCL-on-Si using photoluminescence spectroscopy (PL) will be discussed. This method helped determined the best portion of the remaining material for subsequent processing into ridge waveguide devices.
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Doctor of Philosophy (Ph.D.)
College of Engineering and Computer Science
Electrical and Computer Engineering
Length of Campus-only Access
Doctoral Dissertation (Open Access)
Go, Rowel, "Indium Phosphide Based Quantum Cascade Lasers Grown on Silicon Substrate" (2020). Electronic Theses and Dissertations, 2020-. 218.